This invention relates to concealed magnetic indicia generally and more particularly to a paper token having a magnetic code printed thereon with ink having magnetic particles therein which is overprinted by ink which does not have magnetic particles therein to thereby prevent the copying of the magnetic code by the simple act of utilizing a duplicating machine having magnetic particle copying media therein commonly referred to as "toner."
Concealed indicia has been in wide spread use for many years primarily for the purpose of having the exterior coating Protect the interior coating from wear or damage such as shown by U.S. Pat. No. 3,684,869.
Other patents have shown magnetic layers with a concealing layer thereover such as seen in U.S. Pat. Nos. 4,315,145, 4,511,616 and 4,455,039, however none of these patents discloses a structure where the overprinting ink and the magnetic code ink will be removed by the same solvents nor where the two inks are so physically bonded that attempted removal of the overprinting ink, as by erasing, will remove the magnetic ink. Thus the magnetic ink cannot be revealed for copying by solvents, erasing or physical abrading to reveal the underlying magnetic coating. For if the concealing or overlying coating can be removed, the magnetic coating ca easily be copies on a duplicating machine using magnetic toner, that is a toner having iron oxide particles therein to thereby duplicate the magnetic code.
This is of particular importance when the magnetic ink is used to print a code on a paper token which will be utilized in a magnetic reading machine such as described in U.S. Pat. No. 4,349,111. With a non-magnetic ink printed over the coded ink the paper token could still be read and identified by the machine. However, with the two inks being removed by the same solent or during physical abrading, it is highly unlikely that the overprinted ink will be removable so that the coded ink can be duplicated on a copying machine with magnetic particles.
It is therefore desirable to have a non-magnetic paper token with a magnetic ink code layer thereon overprinted by a non-magnetic ink layer with the two layers being susceptable to the same solvents and with both being simultaneously removed by physical abrading.